1. Field of the Invention
The present invention relates to a coating composition capable of forming a low refractive index layer excellent in the scratch resistance and antifouling property, and a display device used for the image display of a computer, a word processor, a television and the like. More specifically, the present invention relates to an antireflection film, a polarizing plate and a liquid crystal display device, which are effective for enhancing the display quality.
2. Description of the Related Art
In a display device such as cathode ray tube display device (CRT), plasma display panel (PDP), electroluminescence display (ELD) and liquid crystal display device (LCD), an antireflection film is generally disposed on the outermost surface of a display for preventing reduction in contrast or projection of an image due to reflection of outside light and enhancing the visibility of an image by utilizing the principle of light diffusion and optical interference.
The conventional antireflection film includes an antiglare antireflection film of diffusing the surface reflected light to suppress the specular reflection of outside light and prevent projection of an external environment. Also, in the antireflection film of JP-A-2002-196117, one low refractive index layer is provided on an antiglare hard coat layer having a surface fine irregularity structure, whereby in addition to diffusion of outside light on the surface, the reflectance is reduced by utilizing the principle of light interference. In JP-A-2003-75603, an antireflection film not having a surface fine irregularity structure but utilizing only the light interference has been proposed, where a medium refractive index layer, a high refractive index layer and a low refractive index layer are sequentially provided on a substrate film to form a laminate structure.
In the case of reducing the reflectance by utilizing the interference principle as above, it is very effective to decrease the refractive index of the low refractive index layer on the outermost surface. Conventionally, a technique of increasing a fluorine content of the material used or decreasing the density in the layer, for example, by introducing voids has been made to reduce the refractive index of the layer. However, in any attempt, there is caused a problem that the film strength and adhesion to the lower layer are impaired and the scratch resistance is deteriorated. In order to solve this problem, JP-A-2002-317152 has proposed an antireflection film where a low refractive index layer containing a hollow silica fine particle is provided by coating on a hard coat layer and not only the antireflection property is enhanced by the effect of the hollow silica of reducing the refractive index but also the film strength is elevated by virtue of the strength of the hollow silica. In JP-A-2004-272198, a low refractive index layer having an ionizing radiation curing-type nanoporous structure has been proposed.
In these cases, a certain effect of improvement is obtained with respect to the projection of outside light and the scratch resistance, but the antifouling property is insufficient and an antifouling layer must be further provided on the low refractive index layer.
In recent years, various displays are used in a wide-ranging environment and demands for a higher level are increasing, but it can be hardly said that the antireflection property, scratch resistance and antifouling property are all satisfied in a high level to meet the requirements.